The carbonaceous deposit that develops in furnaces when converting hydrocarbons is generally termed coke. This coke deposit is a nuisance in industrial units. The formation of coke on the walls of tubes and reactors causes a reduction in heat exchange, major blockages and thus an increase in pressure drops. In order to keep the reaction temperature constant, it may be necessary to increase the temperature of the walls, which risks damaging the alloy constituting those walls. A reduction in the selectivity of the facilities, and thus a reduction in yield, is also observed.
Japanese application JP-A-03/10 4843 describes a refractory anti-coking steel for an ethylene cracking furnace tube. However, that steel comprises more than 15% of chromium and nickel and at least 0.4% of manganese. That steel was developed to limit coke formation between 750.degree. C. and 900.degree. C. when cracking ethylene. In addition, United States patent U.S. Pat. No. 5,693,155 concerns petrochemical processes using low coking stainless steels. Such steels contain at least 10% of nickel and at least 10% of chromium. Because of those chromium and nickel contents, such steels are more expensive than those of the present invention.